This invention relates generally to pulse generators and, more particularly, to pulse generators that can be easily integrated into monolithic microwave integrated circuits (MMICs). Short duration (i.e., narrow) pulses have practical application in time domain measurement in the terahertz region. For reference, a terahertz (THz) is 1012 hertz, or a thousand gigahertz (GHz). Short pulses are also needed in radar transmitters, high speed sampling applications, and in impulse radio, an emerging technology that requires very narrow pulses with very short rise and fall times. Commercially available pulse generators are less than adequate for advanced microwave, millimeter-wave, radar, or high speed digital sampling applications.
The pulse generator described and claimed in U.S. Pat. No. 6,690,247, entitled “Nonlinear Transmission Line Waveform Generator Having an Input Voltage Matched to the C/V Characteristic of the Transmission Line,” issued in the names of Mark Kintis et al. and assigned to the same assignee as the present application, addressed many of the problems of the prior art but presented implementation difficulties. The disclosure of the referenced patent is incorporated by reference into this description.
Nonlinear transmission lines are generally known in the art. Examples of such nonlinear transmission lines are disclosed in: “GaAs Nonlinear Transmission Lines for Picosecond Pulse Generation and Millimeter Wave Sampling”, by Rodwell, et al., IEEE Transactions on Microwave Theory and Techniques, vol. 39, no. 7, July 1991, pages 1194-1204; U.S. Pat. Nos. 5,352,994; 5,352,627; 5,023,574; 5,256,996; 5,789,994; 5,014,018; and 5,157,361, all of which are also incorporated by reference into this description. Such nonlinear transmission lines are used in various applications, such as harmonic generators and in the generation of relatively short duration narrow pulses in the hundreds of picosecond range, which provide increased bandwidth in certain applications, such as ultra wideband radio applications, also known as impulse radios. Ultra wideband radios, which are generally known in the art, utilize relatively short-duration pulses with pulse widths measured in the hundreds of picoseconds, for example. These short-duration pulses are pulse-position modulated, to increase the bandwidth of such radios up to, for example, 5 GHz. There is an ever increasing demand to increase the bandwidth of such impulse radios, as well as that of other microwave devices. The bandwidth of ultra-wideband radios is limited by the current technology in which the shortest duration pulses that can be generated are on the order of hundreds of picoseconds. To meet the demand for higher bandwidth impulse radios and other applications, there is a need to provide a system for generating pulses having pulse widths less than hundreds of picoseconds in duration.
Accordingly, there is still much room for improvement in the field of time domain pulse generation for MMIC applications. The present invention is directed to that end.